The invention relates to a coating press for sheet-like work-pieces. The coating press contains a press frame with press cylinders, an upper and a lower press platen, at least one pressure plate, a pressure compensating cushion disposed between the press platen and the pressure plate, and a press controller.
A plate press for the coating of plate-shaped work-pieces, contains the press frame with press cylinders, the upper and a lower press platen, the pressure plate and the pressure compensating cushion disposed between the press platen and the pressure plate. Such a plate press is known, Published, Non-Prosecuted German Patent Application DE 199 37 694 A1, in which the pressure compensating cushion contains a diaphragm plate and a compensating plate, solid in the cold state, between the diaphragm plate and a heating plate of the plate press. The compensating plate forms, at the pressing temperature, a liquid pressure pad having a predetermined viscosity and thermal conductivity. The known press is intended to have the effect that, with respect to the pressure plate, there is established a homogeneous pressure distribution and minimized pressure plate wear which is usually caused by the deformations of the press platens as a consequence of thermal stresses and by unevennesses of the work-pieces or by their thickness tolerances generated during the manufacturing process.
One disadvantage of the known solution is that the entire press requires fundamental actions and change in order to integrate the pressure compensation cushion into the press platens, this being extremely inefficient. Furthermore, by virtue of such a special construction, the versatility of a press thus equipped is considerably restricted. Also, the diaphragm plate has to be made relatively thick, so as not to bulge out locally in the case of the supporting zones or anchoring heads lying far apart from one another, with the result that the diaphragm plate cannot mate with the surface of the work-pieces. There is, furthermore, a risk that, in the case of very thin and very hard work-pieces to be coated, there will be formed on the work-piece surfaces nests of approximately the size of the area of a hand, which are not completely pressed, so that such work-pieces are only second-rate or even rejects.
It is accordingly an object of the invention to provide a coating press for sheet-like work-pieces that overcome the above-mentioned disadvantages of the prior art device of this general type, which, along with reduced maintenance intensity, delivers a constantly high-grade working result and which, in particular, is to be capable of compensating small-area unevennesses of the work-pieces. Furthermore, the versatility of the coating press is to be maintained as far as possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a coating press for sheet-like work-pieces. The coating press contains a press frame, press cylinders supported by the press frame, an upper press platen connected to the press cylinders, a lower press platen supported by the press frame, at least one pressure plate, and at least one pressure compensating cushion disposed between the upper press platen or the lower press platen and the pressure plate. The pressure compensating cushion is a hydraulic cushion having a lateral edge closure, a hydraulic medium, and covers including an upper cover and a lower cover. The upper and lower covers along with the lateral edge closure define a pressure-tight inner space filled with the hydraulic medium. A press controller is further provided. Since the pressure compensating cushion is configured as a hydraulic cushion that has an upper cover, a lower cover and a lateral edge closure, and since the covers and the lateral edge closure surround a pressure-tight inner space which is filled with a hydraulic medium, a pressure compensating cushion is made available which can be exchanged in a simple way for a conventional pressure compensating cushion, without substantial actions on the construction of an existing coating press becoming necessary for this purpose. The hydraulic cushion may also advantageously be used in other types of press, such as multistage presses or film-strip presses. The coating press equipped with such a hydraulic cushion allows isobaric pressure distribution to the work-piece, in spite of thermally induced or weight-induced or pressure-induced bending of the press platens or in spite of the large-area thickness tolerances, caused by the grinding process, of the work-pieces to be coated, of about {fraction (1/10)}-{fraction (3/10)} mm. By virtue of the large-area, close configuration of the supporting profiles, in conjunction with an extremely thin work-piece-side cover, even small-format unevennesses of the work-pieces, which occur, for example, due to faults during the process of grinding chipboards, can be ironed out.
It is advantageous, furthermore, that such a coating press allows a continuous change of format of the work-piece in terms of length and width. Moreover, because of the matability of the work-piece-side cover and the isobaric pressure distribution achieved thereby, the work can be carried out with lower specific pressures, so that, in the case of a new construction of a coating press, the frame plates of the press frame, the press platens, the heating plates and the press cylinders can be produced with lighter weight. The known conventional press cushions can be dispensed with completely or else continue to be used in a substantially thinner form for a much longer period of time. In the case of new coating presses, even counter heating of the press platens may be dispensed with. It could be used, for example, simply for better heat distribution. The extra costs that the hydraulic cushion according to the invention generates are then compensated merely by virtue of the absence of manufacturing costs, piping, regulating systems and control for the counter heating.
Further advantages for the manufacturer using a coating press are reliable production, even in the event of stoppages in the process cycle, and the absence of costs due to the press cushion, the absence of service life monitoring, of the necessary cushion changes and also of pressing-in operations.
The hydraulic cushion can be pressurized under a press platen in a similar way to a normal pressure compensating cushion and can consequently be retrofitted in a simple way even on existing presses.
A further essential advantage is that the hydraulic cushion is not tied to any particular press temperature. It may also be used at temperatures of below 100xc2x0 C. or even manage completely without heating. The cushion can therefore be used not only in short-cycle presses, what may be referred to as short cycle (SC) plants, but also in all other types of press.
According to a particularly preferred embodiment of the invention, on the covers of a hydraulic cushion are provided inwardly directed supporting profiles which are connected to one another in a form-fitting manner with mutual play in the vertical direction of the covers, so that a maximum travel of the two covers in relation to one another is fixed via the play. This measure prevents the situation where the internal pressure within the hydraulic cushion that occurs due to the surface pressure bulges out where the cushion is not supported by a work-piece or the situation where the pressure plate may bend away at the edge of the work-piece. In order to ensure that the surface of the cover facing the work-piece can nevertheless mate completely with the surface of the latter in a particularly advantageous way, the cover is made thinner than the cover facing away from the work-piece.
An embodiment is particularly advantageous here in which the supporting profiles of both covers have the same height, so that the profiles of one cover bear on the inside on the other cover and thus make available a large-area support of the covers which, in the event of a fault, such as, for example, the loss or escape of the hydraulic medium, can absorb the full pressure force of the press plates.
The stroke limitation of the two covers can be achieved preferably in that the supporting profiles have lateral projections and undercuts, behind which projections and undercuts of adjacent opposite supporting profiles of the other cover engage with play, so that the supporting profiles are interlocked in a form-fitting manner.
Another advantageous stroke limitation may consist of recesses which are introduced into the supporting profiles transversely to these and through which transverse bars are led, the recesses having in the direction of the covers inner dimensions which are greater than the dimensions of the thickness of the transverse bars, so that, even here, a defined play is generated, the amount of which is equivalent to the maximum possible stroke of the two covers.
In order to prevent the situation where work-piece contours of a frequently manufactured size of a work-piece may press into the pressure plate, it is advantageous to dispose the supporting profiles obliquely at an angle to the right-angled covers.
It is advantageous, furthermore, to have the configuration of a compensating vessel or cylinder for the hydraulic medium, which may preferably be a thermally conductive paste which has the advantage of high thermal conductivity and which tolerates the necessary temperatures over a long service life. Since the hydraulic medium used is impressible, the desired tolerance compensation of the thickness gives rise to a change in volume within the hydraulic cushion which would amount to only one liter in the case of a pressing area of, for example 2xc3x975 m and a thickness change of, for example, {fraction (1/10)} mm.
Advantageously, the compensating cylinder can be acted upon by a regulatable hydraulic pressure, so that, by pressure and quantity regulation of the hydraulic counter pressure, the xe2x80x9celastic spring effectxe2x80x9d of the hydraulic cushion and the desired or permissible thickness compensation value can be finely regulated. Furthermore, by such a system, it is advantageously also possible to generate another surface pressure in the coating press, to be precise when the pressure line to the press cylinders is shut off and the surface pressure is generated only by the compensating cylinder being acted upon by the desired pressure. Furthermore, the nature and speed of the buildup and breakdown of the pressing pressure can advantageously be influenced via the pressure-loaded compensating cylinder. Furthermore, via the press controller of the coating press, the tolerance range can advantageously be set continuously via the maximum amount of play. For this purpose, only the pressure on the volume of the hydraulic counter control in the compensating cylinder has to be controlled correspondingly.
The supporting profiles may have, for example, T-shaped, trapezoidal or z-shaped cross sections, in order to ensure the desired task of preventing the bulging out of the covers of the hydraulic cushion. Furthermore, the supporting profiles may advantageously be made massive or else be produced from bent metal sheets. Moreover, the supporting profiles may be welded, riveted or adhesively bonded to the covers or even be shaped in one piece out of the covers or be milled in these.
Use of the hydraulic cushion does not necessary in this case require a conventional pressure compensating cushion to be dispensed with, although the latter, when used with the coating press according to the invention, is exposed to substantially lower wear-promoting conditions. The conventional pressure compensating cushion may in this case continue to serve for compensating the distribution.
According to particular advantageous embodiments of the invention, the press platens may have a divided configuration and consist, for example, of a separate thrust plate, of insulation and of an adjoining heating plate, on the free side of which the hydraulic cushion and, above the latter, a pressure plate are disposed. The hydraulic cushion may in this case also selectively be integrated in the heating plate, a cushion-related acceptance of insulation thickness differences due to manufacture or to continuous load affording the possibility of configuring the heating plate with a minimum possible thickness according to the necessary bore diameter and of optimizing the insulation for the still relatively low surface pressure. The thrust plate itself may be produced, for example, from a steel plate or from a profile structure. This separate construction results in further major advantages of the coating press, such as, for example, on account of the considerably lower mass of the heating plate, a substantially more dynamic regulating behavior and, consequently, more rapid reaction to production interruptions, moreover substantially shorter heating and cooling times, a possible absence of an otherwise necessary counter heating, along with all its components, and, also, thermal insulation of adjacent press components may be dispensed with, since the frame plates, the press cylinders and the hydraulic oil heat up to a lesser extent, and high-pressure insulation of the press cylinders may also be dispensed with. Furthermore, such a configuration also makes it possible to change the heating system, for example to use direct electrical high-current heating, and makes it possible to have a considerable energy saving.
Further advantageous modifications of the coating press have hydraulic cushions which are subdivided into a plurality of sections sealed off relative to one another and which are connected in each case to the separate compensating cylinder, so that individual regions between the press platens can be activated in an optimized manner. Another embodiment has a plurality of separate hydraulic cushions over the surface of a press platen, so that a mutual dependence of adjacent sections of a hydraulic cushion may likewise be ruled out. By virtue of this measure, the cushion can be adapted, for example, to some fixed chipboard dimensions.
Embodiments without compensating vessels or cylinders for the hydraulic medium can likewise be produced and can have, in the inner space of the hydraulic cushion, pressure capsules which, when external pressure is applied, decrease in volume correspondingly. As a further advantageous variant, an embodiment may be considered in which the hydraulic cushion has an edge closure that is elastically deformable, so that volume compensation as a result of the lateral expansion of the edge closure may take place.
In a further advantageous embodiment of the invention, there is disposed between the upper pressure plate and the upper press platen or cushion an additional diaphragm which generates between the pressure plate and the upper press platen a leak-tight space which is connected to a compensating vessel and into which, in the open state of the press and with the pressure plate sagging, a thermally conductive medium can be introduced, which, when pressure acts upon the press, is again displaced fully into the compensating vessel. By virtue of this measure, the pressure plate can be maintained constantly at a desired temperature.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a coating press for sheet-like work-pieces, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.